1. Field of the Invention
The present invention relates to a CMOS buffer circuit for liquid crystal display (LCD) drivers; more particularly, the present invention relates to an improved architecture for CMOS buffer that is utilized for abruptly varying capacitive loads.
2. Description of the Related Art
Liquid crystal displays (LCDs) in portable electronic equipment are usually controlled by a switch matrix coupling segments of the LCD to buffer drivers. The buffers are used to drive the LCD segments with a stable voltage. However, changing the number and location of the LCD segments connected to the buffers by the switch matrix abruptly changes the capacitive load on the buffers. In order to allow the required large currents to be drawn from the driver circuits, the buffers are dimensioned to satisfy the maximum currents. This results in increased overall power consumption.
Some current solutions suggest using a one stage CMOS operational amplifier as a buffer, where an additional output current is added to the output branches of the CMOS operational amplifier. However, in such solutions, adaptively biased operational amplifier is not able to provide the same amount of extra output current quickly enough, as the speed of the amplifier remains unchanged. Other solutions with better speed use several gain stages and have restricted stability, especially for larger capacitive loads.
Accordingly, there is a need in the art for an improved architecture for a buffer to be used for abruptly varying capacitive loads, which may be faster and may reduced power consumption.